This invention relates to a radar system and, more particularly, to a coherent pulse radar system.
Conventionally, a medium pulse repetition frequency (PRF) radar and a high PRF radar are well known with their aspect that the number of transmitted pulses during a predetermined time increases in order to improve the capability of detecting a target and to obtain velocity information of the target. In a radar system of this kind, since the time period between adjacent transmitted pulses (a pulse-repetition interval) becomes short, there is the disadvantage that target extractive ranges, in which a target is unambiguously measured, becomes short.
To eliminate this disadvantage, it is basically necessary to identify a transmitted pulse from which each target echo is yielded. In a prior art method of this type, two pulse-trains respectively having different pulse-repetition frequencies are transmitted sequentially. Thus, at a receiving portion, a target distance can be unambiguously determined by considering time coincidence of target detections on the basis of the respective pulse-trains. Such a method is disclosed in M. I. Skolnich's, "RADAR HANDBOOK" o.g. McGraw-Hill, Inc. 1970, pages, 19 - 13 to 19 - 17.
However, this method has the following disadvantage:
Double transmitting time is necessary since the two different pulse-trains should be transmitted sequentially and since the target detection operation is needed for each pulse-train, in order to determine a target distance.
On the other hand, in signal processing, it is a conventional technique to use integration processing for a plurality of pulses, to overcome a low S/N ratio of a signal. However, the aforementioned prior art does not fully utilize received pulses in such an integration operation.